airplay not work on LGOled TV using app AppleTV

It would then seem that the file is not in a fully compatible format. File type and codecs are important, but there are more encoding settings that can influence compatibility. If you encoded this file yourself, then consider using a conversion/encoding settings from an Apple TV preset.

I think AirPlay is limited to 1080p max, except for a few special cases with the Apple TV 4K box involved.

What are you trying to AirPlay? Is it a streaming service (which one), or a local file (what format)?

It seems you are trying to AirPlay from the Apple TV app. Correct?

Has the LG TV been added to the Home app, and assigned to a room? That may be needed for AirPlay 2 functionality. Add a HomeKit accessory to the Home app - Apple Support

Can you AirPlay anything else? E.g. screen mirroring the phone’s home screen?

Use AirPlay to stream video or mirror the screen of your iPhone, iPad, or iPod touch - Apple Support

If screen mirroring or streaming isn't working on your AirPlay-compatible device - Apple Support